The invention relates to equipment and a procedure for supporting charging of subscribers with localised service areas in a mobile telecommunications network which comprises a packet radio network. An example of such networks is a combined GSM/GPRS network.
FIG. 1 is a block diagram illustrating a cellular telecommunications network supporting circuit-switched (CS) connections (e.g. Global System for Mobile Communication, GSM) and packet-switched (PS) connections (e.g. General Packet Radio Service GPRS). Circuit-switched connections are shown as solid lines and packet-switched connections are shown as dotted lines. The basic structure of the GSM system comprises two elements: a base station system BSS and a network subsystem NSS. The BSS and mobile stations MS communicate over radio links. In the base station system BSS each cell is served by a base station BTS. A number of base stations are connected to a base station controller BSC, which controls the radio frequencies and channels used by the BTS. Base station controllers BSC are connected to a mobile services switching centre MSC. As regards a more detailed description of the GSM system, reference is made to the ETSI/GSM recommendations and The GSM System for Mobile Communications, M. Mouly and M. Pautet, Palaiseau, France, 1992, ISBN:2-957190-07-7.
The GPRS infrastructure comprises support nodes such as a GPRS gateway support node (GGSN) and a GPRS serving support node (SGSN). The main functions of the GGSN nodes involve interaction with the external data network. The GGSN updates the location directory using routing information supplied by the SGSNs about an MS's path and routes the external data network protocol packet encapsulated over the GPRS backbone to the SGSN currently serving the MS. It also decapsulates and forwards external data network packets to the appropriate data network and handles the billing of data traffic.
The main functions of the SGSN are to detect new GPRS mobile stations in its service area, handle the process of registering the new MSs along with the GPRS registers, send/receive data packets to/from the GPRS MS, and keep a record of the location of the MSs inside its service area. The subscription information is stored in a GPRS register (HLR) where the mapping between a mobile's identity (such as MS-ISDN or IMSI) and the PSPDN address is stored. The GPRS register acts as a database from which the SGSNs can ask whether a new MS in its area is allowed to join the GPRS network.
The GPRS gateway support nodes GGSN connect an operator's GPRS network to external systems, such as other operators' GPRS systems, data networks 11, such as an IP network (Internet) or a X.25 network, and service centres. A border gateway BG provides access to an inter-operator GPRS backbone network 12. The GGSN may also be connected directly to a private corporate network or a host. The GGSN includes GPRS subscribers' PDP addresses and routing information, i.e. SGSN addresses. Routing information is used for tunnelling protocol data units PDU from data network 11 to the current switching point of the MS, i.e. to the serving SGSN. The functionalities of the SGSN and GGSN can be connected to the same physical node.
The home location register HLR of the GSM network contains GPRS subscriber data and routing information and it maps the subscriber's IMSI into one or more pairs of the PDP type and PDP address. The HLR also maps each PDP type and PDP address pair into a GGSN node. The SGSN has a Gr interface to the HLR (a direct signalling connection or via an internal backbone network 13). The HLR of a roaming MS and its serving SGSN may be in different mobile communication networks.
The intra-operator backbone network 13, which interconnects an operator's SGSN and GGSN equipment can be implemented, for example, by means of a local network, such as an IP network. It should be noted that an operator's GPRS network can also be implemented without the intra-operator backbone network, e.g. by providing all features in one computer.
In cellular mobile communications systems, a mobile station may roam freely within the area of the mobile communications network and connect to the base transceiver station signal received best at a given time. Usually, all base transceiver stations provide substantially similar services for the mobile stations in a network. Some base transceiver stations can, however, be defined to provide a certain special service for all mobile stations of the network, e.g. call charges below the normal tariff. The base transceiver station broadcasts a message concerning such a special service on its packet broadcast control channel (PBCCH), whereby mobile subscribers in the area note that they are within a special service area of the network and may take advantage of this service.
Within the context of this application, such special service areas are referred to as localized service areas (LSA) and the support of LSA is called SoLSA. A subscriber having SoLSA service is called a SoLSA subscriber. A mobile station currently having support for SoLSA is said to be in LSA mode. This may mean e.g. that the mobile station indicates to its user that certain special features (like lower rates or extra services) are available, and it uses these features when applicable. The concept of localised service areas (LSA) is the subject matter of references 1 to 3.
FIG. 1 also shows two LSA areas, LSA1 and LSA2. LSA1 consists of cells C1 to C3, and LSA2 consists of cells C9 and C10. It is assumed that the mobile station MS moves, during a call, along path 10 from cell C1 to cell C10. The call is established in an LSA cell (C1). Between cells C1 and C2, the MS moves slightly out of LSA1, in the sense that better coverage would be obtained from cell C7 which is not an LSA cell. However, the handover algorithm favours LSA cells and, consequently, the MS is not handed over to the base station of C7. When the MS crosses cell C4, the call cannot be maintained as an LSA call. When the MS approaches cell C9, it is handed over to the base station of C9 and the call is again treated as an LSA call.
The present invention involves mainly charging-related aspects of SoLSA subscribers. Charging in a GPRS system is defined in reference 4. For charging, a telecommunications network generally comprises a billing system, such as the Billing Centre BC which may be connected to an MSC, as shown in FIG. 1. The network may also comprise dedicated Charging Gateways CG, as shown between the intra-operator backbone network 13 and the billing centre BC. (Alternatively, the dedicated charging gateways can be replaced by distributed functionality resident in the SGSN and GGSN nodes.)
According to reference 4, collecting charging information in a GPRS system can be briefly summarised as follows. Network elements, such as GPRS support nodes (SGSN and GGSN), monitor charging-related events (transmitting data packets, attaching to the network, mobility management, etc.) The network elements send charging data records, or CDRs, to the Billing Centre BC (possibly via Charging gateways CG). CDRs created by SGSN or GGSN nodes are called S-CDRs or G-CDR, respectively. In addition, an M-CDR conveys information on mobility management-related charging events. There are also SMO-CDRs and SMT-CDRs for MS-originated and MS-terminated short messages. For each charging-related event, there is a corresponding item or entry in the CDR. In the terminology of reference 4, the charging-related items are collectively referred to as a “List of Traffic Volumes”. Reference 4 defines a set of rules for opening and closing each type of CDR, and the contents thereof.
A problem with prior art charging systems is that they completely ignore the SoLSA aspects.